diff --git a/src/ClaudeDo.Ui/Views/Islands/DetailsIslandView.axaml b/src/ClaudeDo.Ui/Views/Islands/DetailsIslandView.axaml
index 31607f25..775a25ee 100644
--- a/src/ClaudeDo.Ui/Views/Islands/DetailsIslandView.axaml
+++ b/src/ClaudeDo.Ui/Views/Islands/DetailsIslandView.axaml
@@ -12,10 +12,12 @@
   <DockPanel>
 
     <!-- ── Header (sticky top): id · title · trash/skull · gear — task detail only ── -->
-    <Border DockPanel.Dock="Top" Classes="island-header"
-            IsVisible="{Binding IsTaskDetailVisible}">
-      <detail:TaskHeaderBar/>
-    </Border>
+    <Grid DockPanel.Dock="Top" IsVisible="{Binding IsTaskDetailVisible}">
+      <Grid.RowDefinitions><RowDefinition Height="Auto" SharedSizeGroup="IslandHeader"/></Grid.RowDefinitions>
+      <Border Classes="island-header">
+        <detail:TaskHeaderBar/>
+      </Border>
+    </Grid>
 
     <!-- ── Body: task details (normal), notes editor (notes mode), or prep log (prep mode) ── -->
     <Grid>
diff --git a/src/ClaudeDo.Ui/Views/Islands/ListsIslandView.axaml b/src/ClaudeDo.Ui/Views/Islands/ListsIslandView.axaml
index 5f4db727..a1c99f48 100644
--- a/src/ClaudeDo.Ui/Views/Islands/ListsIslandView.axaml
+++ b/src/ClaudeDo.Ui/Views/Islands/ListsIslandView.axaml
@@ -183,27 +183,30 @@
   <DockPanel LastChildFill="True">
 
     <!-- ── Header ── -->
-    <Border DockPanel.Dock="Top" Classes="island-header">
-      <StackPanel Spacing="4">
-        <TextBlock Classes="heading" Text="{loc:Tr lists.heading}"/>
-
-        <!-- Search row -->
-        <Border Classes="search-wrap" Margin="0,8,0,12">
-          <Grid ColumnDefinitions="Auto,*,Auto" VerticalAlignment="Center">
-            <PathIcon Grid.Column="0" Width="14" Height="14"
-                      Data="{StaticResource Icon.Search}"
-                      Foreground="{DynamicResource TextFaintBrush}"
-                      Margin="2,0,0,0"/>
-            <TextBox  Grid.Column="1" x:Name="SearchBox" Classes="search-inner"
-                      PlaceholderText="{loc:Tr lists.searchPlaceholder}"
-                      Text="{Binding SearchText, Mode=TwoWay}"/>
-            <Border Grid.Column="2" Classes="kbd" Margin="0,0,2,0">
-              <TextBlock Text="{loc:Tr lists.searchKbd}"/>
-            </Border>
-          </Grid>
-        </Border>
-      </StackPanel>
-    </Border>
+    <Grid DockPanel.Dock="Top">
+      <Grid.RowDefinitions><RowDefinition Height="Auto" SharedSizeGroup="IslandHeader"/></Grid.RowDefinitions>
+      <Border Classes="island-header">
+        <StackPanel Spacing="4">
+          <TextBlock Classes="heading" Text="{loc:Tr lists.heading}"/>
+  
+          <!-- Search row -->
+          <Border Classes="search-wrap" Margin="0,8,0,12">
+            <Grid ColumnDefinitions="Auto,*,Auto" VerticalAlignment="Center">
+              <PathIcon Grid.Column="0" Width="14" Height="14"
+                        Data="{StaticResource Icon.Search}"
+                        Foreground="{DynamicResource TextFaintBrush}"
+                        Margin="2,0,0,0"/>
+              <TextBox  Grid.Column="1" x:Name="SearchBox" Classes="search-inner"
+                        PlaceholderText="{loc:Tr lists.searchPlaceholder}"
+                        Text="{Binding SearchText, Mode=TwoWay}"/>
+              <Border Grid.Column="2" Classes="kbd" Margin="0,0,2,0">
+                <TextBlock Text="{loc:Tr lists.searchKbd}"/>
+              </Border>
+            </Grid>
+          </Border>
+        </StackPanel>
+      </Border>
+    </Grid>
 
     <!-- ── No-repo banner — visible until any User list has a linked working dir; no
          dismiss, no persisted state, comes back if the last repo link is removed. ── -->
diff --git a/src/ClaudeDo.Ui/Views/Islands/TasksIslandView.axaml b/src/ClaudeDo.Ui/Views/Islands/TasksIslandView.axaml
index 37b499d7..e03a44bd 100644
--- a/src/ClaudeDo.Ui/Views/Islands/TasksIslandView.axaml
+++ b/src/ClaudeDo.Ui/Views/Islands/TasksIslandView.axaml
@@ -10,64 +10,67 @@
   <DockPanel LastChildFill="True">
 
     <!-- Header -->
-    <Border DockPanel.Dock="Top" Classes="island-header">
-      <Grid ColumnDefinitions="*,Auto">
-        <StackPanel Grid.Column="0" Spacing="4">
-          <TextBlock Classes="eyebrow" Text="{Binding HeaderEyebrow}"/>
-          <TextBlock Classes="display"
-                     Text="{Binding HeaderTitle}"
-                     TextTrimming="CharacterEllipsis"/>
-          <TextBlock Classes="meta"
-                     Foreground="{DynamicResource TextMuteBrush}"
-                     Text="{Binding Subtitle}"
-                     TextTrimming="CharacterEllipsis"/>
-          <ctl:OperationIndicator Status="{Binding PlanningOperation}"/>
-        </StackPanel>
-
-        <StackPanel Grid.Column="1" Orientation="Horizontal" Spacing="4"
-                    VerticalAlignment="Top">
-          <Border Classes="kbd" VerticalAlignment="Center" Margin="0,0,6,0"
-                  IsVisible="{Binding HasStatusPill}">
-            <TextBlock Text="{Binding StatusPill}"/>
-          </Border>
-          <Button Classes="icon-btn" Classes.active="{Binding IsShowingCompleted}"
-                  IsVisible="{Binding !IsNotesList}"
-                  Command="{Binding ToggleShowCompletedCommand}"
-                  ToolTip.Tip="{loc:Tr tasks.showCompletedTip}">
-            <PathIcon Width="15" Height="15" Data="{StaticResource Icon.Eye}"/>
-          </Button>
-          <Button Classes="icon-btn" IsVisible="{Binding IsLetClaudeVisible}"
-                  Command="{Binding LetClaudeHandleCommand}" ToolTip.Tip="{loc:Tr tasks.letClaudeTip}">
-            <PathIcon Width="15" Height="15" Data="{StaticResource Icon.AgentSuggested}"/>
-          </Button>
-          <Button Classes="icon-btn" IsVisible="{Binding IsMergeReviewsVisible}"
-                  Command="{Binding MergeReviewsCommand}" ToolTip.Tip="{loc:Tr tasks.mergeReviewsTip}">
-            <!-- Icon.GitBranch is line-art: stroke-rendered, PathIcon would fill the lines away -->
-            <Viewbox Width="16" Height="16">
-              <Path Classes="icon-stroke" Data="{StaticResource Icon.GitBranch}"/>
-            </Viewbox>
-          </Button>
-          <Button Classes="icon-btn" IsVisible="{Binding IsQuickClaudeVisible}"
-                  Command="{Binding OpenQuickClaudeSessionCommand}" ToolTip.Tip="{loc:Tr tasks.quickClaudeTip}">
-            <PathIcon Width="15" Height="15" Data="{StaticResource Icon.ArrowOut}"/>
-          </Button>
-          <Button Classes="icon-btn" IsVisible="{Binding IsMyDayList}"
-                  Command="{Binding ClearDayCommand}" ToolTip.Tip="{loc:Tr tasks.clearDayTip}">
-            <PathIcon Width="15" Height="15" Data="{StaticResource Icon.Broom}"/>
-          </Button>
-          <Button Classes="icon-btn" IsVisible="{Binding IsMyDayList}"
-                  Command="{Binding ShowPrepLogCommand}" ToolTip.Tip="{loc:Tr tasks.planMyDayTip}">
-            <Viewbox Width="18" Height="18">
-              <Path Classes="icon-stroke" Data="{StaticResource Icon.PlanDay}"/>
-            </Viewbox>
-          </Button>
-          <Button Classes="icon-btn" IsVisible="{Binding !IsNotesList}"
-                  Command="{Binding OpenListSettingsCommand}" ToolTip.Tip="{loc:Tr tasks.listSettingsTip}">
-            <PathIcon Width="15" Height="15" Data="{StaticResource Icon.Settings}"/>
-          </Button>
-        </StackPanel>
-      </Grid>
-    </Border>
+    <Grid DockPanel.Dock="Top">
+      <Grid.RowDefinitions><RowDefinition Height="Auto" SharedSizeGroup="IslandHeader"/></Grid.RowDefinitions>
+      <Border Classes="island-header">
+        <Grid ColumnDefinitions="*,Auto">
+          <StackPanel Grid.Column="0" Spacing="4">
+            <TextBlock Classes="eyebrow" Text="{Binding HeaderEyebrow}"/>
+            <TextBlock Classes="display"
+                       Text="{Binding HeaderTitle}"
+                       TextTrimming="CharacterEllipsis"/>
+            <TextBlock Classes="meta"
+                       Foreground="{DynamicResource TextMuteBrush}"
+                       Text="{Binding Subtitle}"
+                       TextTrimming="CharacterEllipsis"/>
+            <ctl:OperationIndicator Status="{Binding PlanningOperation}"/>
+          </StackPanel>
+  
+          <StackPanel Grid.Column="1" Orientation="Horizontal" Spacing="4"
+                      VerticalAlignment="Top">
+            <Border Classes="kbd" VerticalAlignment="Center" Margin="0,0,6,0"
+                    IsVisible="{Binding HasStatusPill}">
+              <TextBlock Text="{Binding StatusPill}"/>
+            </Border>
+            <Button Classes="icon-btn" Classes.active="{Binding IsShowingCompleted}"
+                    IsVisible="{Binding !IsNotesList}"
+                    Command="{Binding ToggleShowCompletedCommand}"
+                    ToolTip.Tip="{loc:Tr tasks.showCompletedTip}">
+              <PathIcon Width="15" Height="15" Data="{StaticResource Icon.Eye}"/>
+            </Button>
+            <Button Classes="icon-btn" IsVisible="{Binding IsLetClaudeVisible}"
+                    Command="{Binding LetClaudeHandleCommand}" ToolTip.Tip="{loc:Tr tasks.letClaudeTip}">
+              <PathIcon Width="15" Height="15" Data="{StaticResource Icon.AgentSuggested}"/>
+            </Button>
+            <Button Classes="icon-btn" IsVisible="{Binding IsMergeReviewsVisible}"
+                    Command="{Binding MergeReviewsCommand}" ToolTip.Tip="{loc:Tr tasks.mergeReviewsTip}">
+              <!-- Icon.GitBranch is line-art: stroke-rendered, PathIcon would fill the lines away -->
+              <Viewbox Width="16" Height="16">
+                <Path Classes="icon-stroke" Data="{StaticResource Icon.GitBranch}"/>
+              </Viewbox>
+            </Button>
+            <Button Classes="icon-btn" IsVisible="{Binding IsQuickClaudeVisible}"
+                    Command="{Binding OpenQuickClaudeSessionCommand}" ToolTip.Tip="{loc:Tr tasks.quickClaudeTip}">
+              <PathIcon Width="15" Height="15" Data="{StaticResource Icon.ArrowOut}"/>
+            </Button>
+            <Button Classes="icon-btn" IsVisible="{Binding IsMyDayList}"
+                    Command="{Binding ClearDayCommand}" ToolTip.Tip="{loc:Tr tasks.clearDayTip}">
+              <PathIcon Width="15" Height="15" Data="{StaticResource Icon.Broom}"/>
+            </Button>
+            <Button Classes="icon-btn" IsVisible="{Binding IsMyDayList}"
+                    Command="{Binding ShowPrepLogCommand}" ToolTip.Tip="{loc:Tr tasks.planMyDayTip}">
+              <Viewbox Width="18" Height="18">
+                <Path Classes="icon-stroke" Data="{StaticResource Icon.PlanDay}"/>
+              </Viewbox>
+            </Button>
+            <Button Classes="icon-btn" IsVisible="{Binding !IsNotesList}"
+                    Command="{Binding OpenListSettingsCommand}" ToolTip.Tip="{loc:Tr tasks.listSettingsTip}">
+              <PathIcon Width="15" Height="15" Data="{StaticResource Icon.Settings}"/>
+            </Button>
+          </StackPanel>
+        </Grid>
+      </Border>
+    </Grid>
 
     <!-- Add-task row -->
     <Border DockPanel.Dock="Top" Classes="add-task" Margin="16,14,16,8"
diff --git a/src/ClaudeDo.Ui/Views/MainWindow.axaml b/src/ClaudeDo.Ui/Views/MainWindow.axaml
index 9aad5ade..a053c0ab 100644
--- a/src/ClaudeDo.Ui/Views/MainWindow.axaml
+++ b/src/ClaudeDo.Ui/Views/MainWindow.axaml
@@ -142,7 +142,8 @@
     </Border>
 
     <!-- Three islands (user-resizable) -->
-    <Grid Grid.Row="1" Margin="7">
+    <!-- Shared-size scope: the island headers share one height so their separators line up -->
+    <Grid Grid.Row="1" Margin="7" Grid.IsSharedSizeScope="True">
       <Grid.ColumnDefinitions>
         <ColumnDefinition Width="260" MinWidth="200"/>
         <ColumnDefinition Width="Auto"/>